Deflation device

Abstract

A device is provided which can be screwed onto the adaptor of the valve assembly of a pneumatic tire and a plunger depressed to commence tire deflation. A pressure sensitive member responds to a drop in the pressure of the emerging air to allow the valve to close when a predetermined low pressure remains in the tire.

Having now described our invention, what we claim is: 
     
       1. A device for use in conjunction with an inflation valve including valve closing biasing means of a pneumatic tire for automatically deflating said tire to a predetermined above atmospheric reduced pressure level comprising: a housing including an internally threaded end portion adapted to be connected to external threads on said inflation valve,   a displaceable plunger assembly mounted within said housing and having a first manually operable portion which projects outside said housing and a second portion which is adapted to operatively engage with and open said inflation valve against the force of said biasing means associated therewith when said housing is connected to said inflation valve and an exterior force is applied to said first manually operable portion to move said plunger assembly in an inflation valve opening direction,   a passage within said plunger assembly for allowing air entering said internally threaded end portion to pass therethrough,   a pressure chamber receiving said air exiting from said passage, said chamber being defined by a portion of the interior of said housing and by a surface integral with said plunger assembly, said chamber including a continuously open restricted air passageway communicating with the atmosphere, said plunger assembly surface being sensitive to air pressure in said chamber for urging said plunger assembly in an inflation valve opening direction as long as air pressure within said chamber remains above a predetermined value and for allowing said plunger to be urged in an inflation valve closing direction by said inflation valve biasing means when said housing is connected to said inflation valve and air pressure in said chamber falls below said predetermined value, the dimensions of said restricted air passageway and said integral plunger assmebly surface being such that said predetermined value of air pressure which allows said biasing means to close said inflation valve corresponds to said predetermined above atmospheric reduced pressure level.   
     
     
       2. A device as claimed in claim 1 wherein said plunger comprises separate piston and button portions slidable in said housing in coaxial relation, said button portion being accessible from outside said housing initially to depress said plunger in an inflation valve opening direction. 
     
     
       3. The combination as claimed in claim 1, wherein a locking mechanism is provided which is adapted to prevent the biasing means of said tire valve from urging said plunger in an inflation valve closing direction when said air pressure in said chamber falls below said predetermined value.